The transmission of mitochondria to daughter cells is an essential feature of cell proliferation, yet only a few of the components that mediate mitochondrial division and inheritance have been described. The goal of the proposed study is to understand the molecular mechanisms that facilitate mitochondrial movement during mitotic cell growth, regulated mitochondrial distribution in the cell, and catalyze changes in mitochondrial morphology. This investigation will employ a combined biochemical and genetic analysis using the budding yeast, Saccharomyces cerevisiae, and fission yeast, Schizosaccharomyces pombe, as model cellular systems. The first specific aim will be to identify proteins that interact with an established inheritance component, Mdm1p, to mediate mitochondrial distribution in S. cerevisiae. Interacting proteins will be identified through the isolation and characterization of genetic suppressors and via the purification and analysis of two key proteins of the mitochondrial outer membrane. The second objective is to isolate new mdm mutants displaying defects in mitochondrial distribution and morphology. Genes defined by the mutations will be cloned and their products will be localized in the cell by immunological and microscopic techniques. Additionally, the interaction of these proteins with mitochondria and other cellular structures will be assessed. The third specific aim is to identify novel proteins that mediate the fission of mitochondrial tubules. Proteins that interact with a recently discovered fission component, Gag3p, will be identified, and a gene required for mitochondrial fission, GA G2, will be isolated and its product characterized. A fourth specific objective is to identify and characterize products of mmd1+, mmd2+, and mmd3+, S. pombe genes defined by mmd mutations that cause defects in mitochondrial distribution. The Mmd proteins will be localized in fission yeast cells, and the proteins' interactions with mitochondria, microtubules, and other cellular structures will be assessed. The fifth specific aim is to isolate novel S. pombe mmd mutants. Subsequent analysis will focus on the use of these mutants to identify proteins that mediate the interaction of mitochondria with microtubules. These studies will provide new insights into cellular structure and organelle dynamics, and contribute to an understanding of changes in mitochondrial morphology and distribution that occur in certain pathological conditions such as cancer and heart disease.